Testsuite: T9099: harden GRUB console-select navigation with expect() checks

BOOTLOADERchooseSerialConsole() sent fixed DOWN/ENTER keystrokes with blind
sleeps to navigate the post-install GRUB "Boot options" and "Select console
type" submenus. Under host load, a dropped keystroke could land navigation one
level too deep (e.g. "Select boot mode" instead of "Select console type").

GRUB submenus never time out on their own, so the VM sat there until the
unrelated 600s login wait in loginVM() expired, producing a confusing
pexpect.TIMEOUT far from the real cause.

Add child.expect() checks after each submenu transition to confirm the expected
menu actually rendered before sending the next keypress, so a misnavigation now
fails fast and points at the right step.

Author: c-po

scripts/check-qemu-install

@@ -599,11 +599,19 @@ def BOOTLOADERchooseSerialConsole(child, live: bool) -> None:
         time.sleep(BOOTLOADER_SLEEP)
         child.send(KEY_RETURN)
         time.sleep(BOOTLOADER_SLEEP)
+        # GRUB submenus never time out on their own, so confirm we actually
+        # landed on this submenu before navigating further - otherwise a
+        # dropped keypress leaves the VM stuck here until the login wait
+        # elsewhere expires
+        child.expect('Select console type', timeout=BOOTLOADER_TMO)
+
         # Select console type
         child.send(KEY_DOWN)
         time.sleep(BOOTLOADER_SLEEP)
         child.send(KEY_RETURN)
         time.sleep(BOOTLOADER_SLEEP)
+        child.expect(r'ttyS \(serial\)', timeout=BOOTLOADER_TMO)
+
         # *ttyS (serial)
         child.send(KEY_DOWN)
         time.sleep(BOOTLOADER_SLEEP)